International Monetary Fund chief Christine Lagarde on Friday warned that the global economy was slowing, with a soon-to-be published growth outlook lower than earlier forecasts.

"What I can tell you is that it will be tilted to the downside and certainly lower than the forecast that was published three months ago," she told an economic forum in Tokyo.

In April, the IMF hiked its global growth forecasts to an annual rate of 3.5 percent this year, accelerating to 4.1 percent in 2013, up from the January forecast of 3.3 percent and 4.0 percent respectively.

Lagarde declined to elaborate on its upgraded assessment due later this month but said that the outlook since the last IMF forecast had "regrettably" become "more worrisome".

The IMF had said its improved global forecast in April was due in part to better global financial conditions and easing fears about the eurozone debt crisis.

"The outlook for the global economy is slowly improving again but is still very fragile," it said at the time.

On Tuesday, the Washington-based IMF cut its growth forecast for the US economy and warned that the Obama administration could be slicing the deficit too fast for the weak economy.

The IMF estimated 2012 US economic growth at 2.0 percent, down from an April forecast of a 2.1 percent expansion for the world's biggest economy.